Flat-panel display and flat-panel display cathode manufacturing method

ABSTRACT

A flat-panel display includes a front glass, glass substrate, cathodes, gate electrodes, phosphor films, and anodes. The front glass has translucency at least partly. The substrate is placed to oppose the front glass through a vacuum space. The cathodes are formed on the substrate. The gate electrodes are placed in the vacuum space and spaced apart from the cathodes. The phosphor layers and anodes are formed on a surface of the front glass which opposes the substrate. Each cathode includes a metal member having many opening portions which is mounted on the substrate, and a conductive material containing carbon nanotubes filled in the mesh-like opening portions. A method of manufacturing a flat-panel display is also disclosed.

BACKGROUND OF THE INVENTION

The present invention relates to a flat-panel display which emits lightby bombarding electrons emitted from a field emission electron sourceagainst a phosphor and a method of manufacturing a flat-panel displaycathode.

As one of the electron display devices, a flat-panel display such as anFED (Field Emission Display) or flat fluorescent display tube isavailable, which emits light by bombarding electrons emitted from anelectron-emitting source serving as a cathode against a light-emittingportion formed from a phosphor formed on a counterelectrode. Recently,an electron-emitting source using carbon nanotubes has been proposed asan electron-emitting source for such a flat-panel display. In aconventional flat-panel display using carbon nanotubes aselectron-emitting sources, a paste containing carbon nanotubes isprinted on a cathode wiring layer formed on a substrate and used as acathode.

In the above conventional flat-panel display, however, cathodes formedby printing vary in thickness or a surface undulation occurs, resultingin failure to form flat cathodes. In such a case, when field electronemission is caused by using parallel electric fields, the electricfields are not uniformly applied between the cathodes or within thecathode surfaces, resulting in the nonuniform amount of electronsemitted. This causes luminance irregularity. In addition, local electronemission occurs to make the electron emission amount unstable, causing aluminance variation.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a flat-panel displaywhich is free from luminance irregularity even if cathodes are formed byprinting a paste containing carbon nanotubes, and a method ofmanufacturing the flat-panel display.

In order to achieve the above object, according to the presentinvention, there is provided a flat-panel display comprising a frontglass having translucency at least partly, a substrate placed to opposethe front glass through a vacuum space, a cathode formed on thesubstrate, a gate electrode placed in the vacuum space and spaced apartfrom the cathode, and a phosphor layer and an anode formed on a surfaceof the front glass which opposes the substrate, wherein the cathodeincludes a metal member having many opening portions and mounted on thesubstrate, and a conductive material containing carbon nanotubes filledin the mesh-like opening portions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view showing the main part of a flat-paneldisplay according to the first embodiment of the present invention;

FIG. 1B is a sectional view of a cathode portion in FIG. 1A;

FIG. 2 is a partial sectional view taken along the direction indicatedby an arrow A in FIG. 1A;

FIGS. 3A to 3D are sectional views showing a method of manufacturingcathodes;

FIG. 4 is a perspective view for explaining a method of assembling theflat-panel display in FIGS. 1A and 1B; and

FIG. 5 is a perspective view showing the main part of a flat-paneldisplay according to the second embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described in detail below with referenceto the accompanying drawings.

FIGS. 1A and 1B show the arrangement of a flat-panel display accordingto the first embodiment of the present invention. As shown in FIG. 1A,the flat-panel display according to this embodiment includes a glasssubstrate 101 having a substantially rectangular shape when viewed fromthe top, a transparent front glass 103 which is placed to oppose theglass substrate 101 at a predetermined distance and has a substantiallyrectangular shape when viewed from the top, and a frame-like spacerglass 107 placed on the peripheral portions of these components. Thespacer glass 107 is bonded to the peripheral portions of the glasssubstrate 101 and front glass 103, which are placed to oppose eachother, with low-melting frit glass to form an envelope. The envelope isheld at a vacuum degree of 10⁻⁵ Pa. Low alkaline soda glass is used forthe glass substrate 101, front glass 103, and spacer glass 107 whichconstitute the envelope. Plate glass members each having a thickness of1 to 2 mm are used as the glass substrate 101 and front glass 103.

A plurality of substrate ribs 102 which are parallel to each other areformed on one surface of the glass substrate 101 at predeterminedintervals. The surface of the glass substrate 101 is partitioned into aplurality of areas isolated from each other by the substrate ribs 102.As shown in FIG. 1B, strip-like cathodes 110 each having a width equalto the interval between the ribs are formed in the areas on the glasssubstrate 101 which are sandwiched between the substrate ribs 102 tohave the same height (thickness) as that of the substrate rib 102. Thesubstrate rib 102 is an insulator having a rectangular cross-sectionwhich is formed by repeatedly screen-printing an insulating pastecontaining low-melting frit glass on the glass substrate 101 until itreaches a predetermined height (thickness) and then calcining the paste.

The cathode 110 is comprised of a mesh-like metal plate 111 having manymesh-like opening portions 111 a and electron-emitting portions 112formed in the mesh-like opening portions 111 a. The electron-emittingportions 112 in the mesh-like opening portions 111 a are formed suchthat their thicknesses are almost uniform and their surfaces do notprotrude from the mesh-like opening portions 111 a. The height of thesubstrate rib 102 is set to be equal or smaller than that of themesh-like metal plate 111 so that the interval between theelectron-emitting portion 112 and a conductive film 121 (to be describedlater) serving as a gate electrode can be defined by only a spacermember.

More specifically, the height of the substrate rib 102 is preferably setto be equal to that of the mesh-like metal plate 111 or smaller thanthat by at least 0.05 mm in order to prevent electric discharge betweenitself and the mesh-like metal plate 111. In this embodiment, asdescribed above, the height of the mesh-like metal plate 111 was set tobe equal to that of the substrate rib 102, the pitch of the substrateribs 102 was set to 1 to 2 mm, and the width of the substrate rib 102was set to 0.05 mm.

A plurality of front-surface ribs 104 are formed upright on the oppositesurface of the front glass 103 to the glass substrate 101 atpredetermined intervals in a direction perpendicular to the arraydirection of the substrate ribs 102 and cathodes 110. Strip-likephosphor films 105B, 105G, and 105R are repeatedly formed on the surfaceof the front glass 103 so as to be arranged one by one in each areasandwiched between the front-surface ribs 104. Metal-backed films 106serving as anodes are formed on the phosphor films 105B, 105G, and 105R(the opposite surfaces to the glass substrate 101). The front-surfacerib 104 is an insulator having a rectangular cross-section which isformed by repeatedly screen-printing an insulating paste containinglow-melting frit glass at a predetermined position on the inner surfaceof the front glass 103 until it reaches a predetermined height and thencalcining the paste.

The phosphor films 105B, 105G, and 105R are made of phosphors havingpredetermined emission colors and formed by screen-printing phosphorpastes of the respective colors on the surface of the front glass 103 ina striped pattern and calcining the pastes. The phosphor film 105R is ared emission phosphor film using a red emission phosphor used for redlight. The phosphor film 105G is a green emission phosphor film using agreen emission phosphor used for green light. The phosphor film 105B isa blue emission phosphor film using a blue emission phosphor used forblue light. These phosphor films are repeatedly formed in the order ofthe phosphor film 105R for red light, the phosphor film 105G for greenlight, and the phosphor film 105B for blue light.

A known oxide phosphor or sulfide phosphor which emits light bybombardment of electrons accelerated by a high voltage of 4 to 10 kV,which is generally used for a cathode ray tube or the like, can be usedfor the phosphor films 105R, 105G, and 105B for R, G, and B light beams.In this embodiment, three types of phosphor films which emit light beamsof the primary colors, i.e., R, G, and B, are used for color display.However, the present invention is not limited to this, and one type ofphosphor film may be used for monochrome display. The metal-backed films106 are made of thin aluminum films each having a thickness of about 0.1μm and formed on the surfaces of the phosphor films 105R, 105G, and 105Bby using a known vapor deposition method.

Insulating spacers 120 each having a rectangular cross-section arearranged between the substrate ribs 102 and cathodes 110 on the glasssubstrate 101 and the front-surface ribs 104 of the front glass 103 incorrespondence with the front-surface ribs 104. The insulating spacer120 is formed from a 0.3-mm thick alumina substrate in which electronpassage slits are formed at a predetermined pitch. The slits are formedby using a laser beam. Note that the insulating spacer 120 is notlimited to an alumina. substrate, and another ceramic substrate or glasssubstrate may be used. Obviously, the thickness of the insulating spacer120 and the slit width can be changed as needed.

The insulating spacer 120 is wider than the front-surface rib 104 andplaced such that the center line of the insulating spacer 120 coincideswith that of the corresponding front-surface rib 104. As shown in FIG.2, one pair of striped gate electrodes 121 are formed on the end face ofthe insulating spacer 120 on the two sides of the front-surface rib 104.The insulating spacer 120 is pressed by the atmospheric pressure andfixed between the front-surface rib 104 and the mesh-like metal plate111. The insulating spacers 120 support the front glass 103 via thefront-surface ribs 104 and also support the gate electrodes 121 apartfrom the cathode 110.

The front-surface rib 104 has a height that sets a gap of 2.0 to 4.0 mmbetween the gate electrodes 121 and the metal-backed film 106, and thepitch of the front-surface ribs 104 is set to be the same as that of thesubstrate ribs 102. Note that the front-surface rib 104 is not limitedto this. The width of the front-surface rib 104 may be so set as toprevent breakdown between the adjacent metal-backed films 106 and theadjacent gate electrodes 121 and support the atmospheric pressure. Theheight of the front-surface rib 104 may be changed in accordance withthe anode voltage applied to the metal-backed film 106. In addition, theintervals between the ribs may be changed as needed.

The gate electrode 121 is a conductive film which is formed byscreen-printing a conductive paste containing silver or carbon as aconductive material into a striped pattern having a thickness of about10 μm on the insulating spacer 120 and calcining the paste. In thisembodiment, the gate electrode 121 is formed from a striped conductivefilm formed on the insulating spacer 120. However, the gate electrode121 is not limited to this. For example, ladder- or mesh-like thin metalfilms may be formed to oppose the phosphor films 105B, 105G, and 105Rand supported by the insulating spacers 120 to be spaced apart from theelectron-emitting portions 112.

The mesh-like metal plate 111 protrudes outside through the envelope andserves as a cathode lead for externally applying a cathode voltage. Eachgate electrode 121 is connected to a corresponding gate electrode lead(not shown) extending through the envelope. A predetermined controlvoltage is externally applied to each gate electrode 121. Themetal-backed film 106 is connected to one anode lead (not shown)extending through the envelope. An anode voltage for acceleratingelectrons is externally applied to the metal-backed film 106.

The mesh-like metal plate 111 which constructs the cathode 110 is formedfrom a mesh-like thin metal plate having regular hexagonal meshes. Forexample, a stainless steel plate having a thickness of 0.1 to 0.15 mm isetched to form mesh-like through holes each having an opening size (thedistance between opposite sides) of 0.1 to 1.0 mm with the openingportion 111 a having a regular hexagonal shape. Note that the shape ofthe opening portion 111 a of the mesh-like metal plate 111 is notlimited to a regular hexagonal shape. For example, the mesh-like metalplate 111 may be formed into a ladder-like pattern having rectangularthrough holes formed at predetermined intervals. Alternatively, theopening portion 111 a may be formed into a polygonal shape such as atriangular or rectangular shape, a polygonal shape with round corners,or a circular or elliptic shape.

The electron-emitting portion 112 is a field emission electron sourcewhich emits electrons upon application of a high electric field. Theelectron-emitting portion 112 is formed by filling the opening portion111 a of the mesh-like metal plate 111 with a conductive pastecontaining carbon nanotubes by printing. This electron-emitting portion112 is comprised of a conductive film filled in the opening portion 111a of the mesh-like metal plate 111 and many carbon nanotubes exposedfrom the surface of the conductive film. The surface of the conductivefilm is exposed in the opening portion 111 a of the mesh-like metalplate 111, and the many carbon nanotubes exposed from the conductivefilm surface function as an electron-emitting source.

Each carbon nanotube has a structure in which a single graphite layer isclosed into a cylindrical shape, and a five-membered ring is formed onthe distal end portion of the cylinder. The carbon nanotube has a smalldiameter of 4 to 5 nm, and hence can emit electrons by field emissionupon application of an electric field of about 100 V. Note that thestructures of carbon nanotubes include a single-layer structure and acoaxial multilayer structure in which a plurality of graphite layers arestacked in a nesting pattern and each graphite layer is closed into acylindrical shape. Either of the structures can be used. Alternatively,a hollow graphite tube having a defect due to structural disturbance ora graphite tube filled with carbon may be used.

In the flat-panel display having the above arrangement, a potentialdifference is set between the cathode 110 and the gate electrode 121such that a positive potential is set at the gate electrode 121. Withthis setting, an electric field concentrates on the carbon nanotubes ofthe electron-emitting portion 112 at the intersection of the gateelectrode 121 and cathode 110. As a consequence, a high electric fieldis applied to the carbon nanotubes, which in turn emit electrons fromtheir distal ends. In this case, when a positive voltage (acceleratingvoltage) is applied to the metal-backed film 106, the electrons emittedfrom the electron-emitting portion 112 are accelerated toward to themetal-backed film 106. The accelerated electrons are transmitted throughthe metal-backed film 106 and collide with the phosphor films 105B,105G, and 105R. The phosphor films 105B, 105G, and 105R then emit light.

Assume that an n×m dot matrix display unit is formed by forming n gateelectrodes 121 in the row direction, and m cathodes 110 in the columndirection. In this case, while a positive voltage (accelerating voltage)is applied to the metal-backed film 106, a positive voltage is appliedto the gate electrode 121 in the first row, and a negative voltage isapplied to the first to mth cathodes 110 to sequentially scan thedisplay addresses in the first to mth columns. This operation isrepeated from the first to nth gate electrodes 121 to perform dot matrixdisplay. In this case, 0 V is applied to the cathodes 110 and gateelectrodes 121 to which no voltage is applied, or a negative biasvoltage of several V with respect to the cathodes 110 is applied to thegate electrodes 121 to prevent the electron-emitting portions 112 otherthan those at the display addresses from emitting electrons.

In addition, 0 V and a position voltage may be applied to the cathode110 in such a manner that 0 V is applied to it to emit light, and apositive voltage is applied to it to emit no light. In this case, withregard to the gate electrodes 121, an active row is held at a positivevoltage, and 0 V or a negative bias voltage of several V is applied tothe remaining rows to prevent the electron-emitting portions 112 otherthan those at the display addresses from emitting electrons. In thisembodiment, the voltage applied to the metal-backed film 106 was set to6 kV, the voltages applied to the gate electrode 121 were set to 500 Vand 0V, and the voltages applied to the gate electrode 121 were wet to500 V and 0 V. In this case, since no negative voltage is used, nonegative voltage source is required, resulting in a reduction in cost.

A method of manufacturing the flat-panel display having the abovearrangement will be described next.

[Formation of Cathodes]

First of all, as shown in FIG. 3A, the substrate ribs 102 are formed onthe glass substrate 101 at predetermined intervals. The substrate rib102 is formed by repeatedly screen-printing an insulating pastecontaining low-melting frit glass on the glass substrate 101 until itreaches a predetermined height and then calcining the paste.

As shown in FIG. 3B, the mesh-like metal plates 111 are stuck on theglass substrate 101 between the adjacent substrate ribs 102. As shown inFIG. 3C, after a print screen 115 is stuck on the mesh-like metal plates111, each mesh-like opening portion 111 a of the mesh-like metal plates111 is filled with a conductive paste 116 containing carbon nanotubes byscreen printing. In this case, the print screen 115 has print patterns117 exhibiting one-to-one correspondence with the opening portions 111 aof the mesh-like metal plates 111. The print pattern 117 has a planarshape similar to the shape of the opening portion 111 a and the samesize as that of the opening portion 111 a or a size reduced at apredetermined ratio.

As the conductive paste 116 containing carbon nanotubes, a pasteobtained by kneading a needle-shaped bundle (columnar graphite) having alength of several 10 μm and mainly containing carbon nanotubes with asilver paste (a conductive viscous solution) at a mixing ratio of 1:1 isused. The silver paste is a paste having fluidity which is obtained bydispersing glass particles with a particle diameter of about 1 μm andsilver particles with a particle diameter of about 1 μm in a viscousvehicle dissolved by using a resin as a solvent. As the vehicle, amaterial that easily dissolves and volatilizes is used. The vehicle isremoved by heating the paste in the atmosphere at about 300 to 400° C.In addition, as the glass particles, particles that dissolve at about300 to 400° C. are used.

The print screen 115 is then removed, and the resultant structure isheated at about 450° C. for a predetermined period of time to calcinethe conductive paste containing carbon nanotubes in each mesh-likeopening portion 111 a. With this process, a conductive film containing abundle in each mesh-like opening portion 111 a is formed. Since openingportions each having a small opening diameter of 0.1 to 1.0 mm areformed in this conductive film, when glass particles melt upon beingheated in the calcining process, no surface undulation occurs, and thesurface is uniformly planarized. As a consequence, a flat conductivefilm with little variation in thickness can be obtained.

The surface of the conductive film is then irradiated with a laser beamto selectively remove silver particle and binder on the surface byevaporation, thereby exposing the bundles. At the same time, only thecarbon nanotubes are uniformly exposed from the surface of theconductive film by selectively removing polyhedral carbon particles as acarbon component other than carbon nanotubes on the bundle surfaces.Note that the method of exposing carbon nanotubes from the surface of aconductive film is a known method as indicated by FIGS. 7A to 7F in U.S.Pat. No. 6,239,547.

With this process, carbon nanotubes are distributed on only the surfacesof many mesh-like opening portions 111 a, and as shown in FIG. 3D, thecathode 110 having the electron-emitting portions 112 formed from carbonnanotubes is formed on the glass substrate 101.

[Assembly of Flat-Panel Display]

As shown in FIG. 4, the insulating spacers 120 on which the gateelectrodes 121 are formed are mounted on the glass substrate 101 onwhich the cathodes 110 are formed with the gate electrodes 121 facingup. At this time, the insulating spacers 120 are so arranged as to makethe gate electrodes 121 become perpendicular to the cathodes 110.

After the frame-like spacer glass 107 is mounted on the peripheralportion of the glass substrate 101, the front glass 103 on which thephosphor films 105B, 105G, and 105R, metal-backed films 106, andfront-surface ribs 104 are formed is mounted on the spacer glass 107. Atthis time, the front glass 103 is placed on the insulating spacers 120such that the lower end face of each front-surface rib 104 is sandwichedbetween one pair of gate electrodes 121. The glass substrate 101, frontglass 103, and spacer glass 107 are then bonded/fixed with low-meltingfrit glass to form an envelope. An exhaust port (not shown) formed inthe spacer glass 107 is connected to a vacuum pump to evacuate theenvelope to a predetermined pressure. The exhaust port is then sealed.

FIG. 5 shows the structure of a flat-panel display according to thesecond embodiment of the present invention. As in this embodiment,front-surface ribs 104 may be formed in a direction perpendicular toinsulating spacers 120. In this case, gate electrodes 122 formed on theinsulating spacers 120 are formed from split electrodes which are splitby the front-surface ribs 104 in the longitudinal direction of theinsulating spacers 120 and electrically connected to each other.

In the above embodiment, the surface of the conductive film in eachmesh-like opening portion 111 a is irradiated with a laser beam toexpose carbon nanotubes. However, a method of exposing carbon nanotubesis not limited to the laser beam irradiation method. For example, carbonnanotubes may be exposed by selective dry etching using a plasma. Inaddition, the glass substrate is used as a component of the envelope.However, a ceramic substrate or the like may be used.

Furthermore, the conductive paste 116 is obtained by kneading carbonnanotube bundles with a silver paste at a mixing ratio of 1:1. However,they may be kneaded at a different mixing ratio. Although a silver pasteis used as the conductive paste 116 containing carbon nanotubes, otherconductive pates may be used. For example, a conductive paste usingsilver/copper alloy particles may be used. Alternatively, a conductivepolymer may be used.

As has been described above, according to the present invention, sinceconductive films containing carbon nanotubes serving aselectron-emitting sources are formed in the mesh-like opening portionsof mesh-like metal members that are processed to have a uniformthickness, the conductive films are planarized to have a uniformthickness. With this structure, uniform electric fields are applied tothe carbon nanotubes, and electrons are uniformly emitted by fieldemission regardless of the positions. Therefore, uniform field electronemission is realized, and uniform luminance is obtained regardless ofthe pixels.

1. A method of manufacturing a flat-panel display circuit, comprisingthe steps of: sticking a metal plate having mesh-like opening portionson a substrate forming a flat-panel display; filling the mesh-likeopening portion with a conductive material containing carbon nanotubes;and exposing the carbon nanotubes from a surface of the conductivematerial which is exposed in the mesh-like opening portion.
 2. A methodaccording to claim 1, wherein the step of filling comprises the step ofsticking a print screen having print patterns corresponding to themesh-like opening portions on the metal plate and then printing theconductive material containing carbon nanotubes.
 3. A method accordingto claim 1, further comprising the step of calcining the conductivematerial filled in the mesh-like opening portion.
 4. A method accordingto claim 3, wherein the step of exposing comprises the step ofirradiating a surface of the calcined conductive film with a laser beam.